This invention generally relates to coating of a substrate with a powdered, thermoplastic material. More particularly, this invention relates to such coating wherein the powdered material is heated as it is applied to the substrate. Specifically, this invention relates to a spraying apparatus having no moving parts but rather using two series connected fluid amplifiers and an inlet air heater section to supply heated, powdered material to the substrate.
It has long been known that spraying heated thermoplastic materials onto a surface to be coated is a desirable coating technique. Such a system allows quite uniform coating thickness and very good flow out characteristics. However, conventional spray guns which use needles to shut off or control the material flow through them have not been completely successful. In addition, the heating of the powdered material prior to its application has also presented problems since the material once heated tends to stick to the interior of this application apparatus. I have solved these problems by using two fluid amplifiers connected in series to first inspirate the powdered material and cool outside air, and then move outside air which is heated as it is inspirated. The result of this arrangement is that the inlet for the powdered material is remote from the heating location and the heated powdered material tends to flow in a form of air pipe and does not touch the walls of the apparatus.